1. Field of the Invention
The present invention relates to welding practice, and more specifically to a method of surfacing to form a surface layer having different-composed portions, and an apparatus for controlling the same. The invention can be used for surfacing any articles with the formation of a surface layer having certain portions of predetermined composition, for instance, for surfacing rollers to form a surface layer thereon consisting of portions having different composition and, hence, different properties.
2. Prior Art
Known in the art is a method of surfacing to form a surface layer with different-composed portions (cf. USSR Author's Certificate No. 507428) wherein electrode material and filler material, both in the form of two or more rods, are fed to the weld pool in a predetermined order and with a varying speed.
However, the above method has a limited application which is accounted for by limited possibilities in alloying the filler wire due to difficulties associated with drawing difficult-to-deform alloyed wire, and especially in the case of filler wire alloyed with elements raising hardness and lowering plasticity thereof, such as, for instance, carbon.
The degree of alloying of surfacing metal and possibilities of varying the composition and, hence, the properties thereof in the course of surfacing by the prior art method can be considerably enhanced by varying the feed mass velocity (V.sub.m) of filler materials. In this case, however, a part of the heat generated by the arc is consumed to melt down the filler material, which affects the heat balance in the melt pool and, hence, the formation of the surface layer, and may be a cause of a lack of fusion with the basic material.
There is also known an apparatus for controlling the surfacing processes using at least two materials with the ratio of the amount of one material to the other one being maintained by varying their feeding rate or consumption (cf. U.S. Pat. No. 3,931,787). This apparatus has been disclosed in terms of its application for controlling the rate of feeding the flux onto a strip material. It comprises a strip material driving means, a strip material flow rate transducer, flux feeding means, and a feed rate transducer. It also includes a feed rate controlling means, an adder unit for stabilizing rate of feed, and signal converters.
The above apparatus is capable of maintaining only preset ratio of materials with a constant total quantity thereof. When the ratio of materials is changed, for instance, for the purpose of forming a layer having different-composed portions, the total quantity of the materials used also changes, which results in irregular depth of the surface layer being formed.